I've had real problems with all the wireless extenders I've had to play with, and I'd be loathe to suggest anyone try it
My experience is you're better off setting up a second wireless network using an access point, connected to the main router / AP by cable or else ethernet over power plugs.
In this case I'd run a network cable from the Skybox out to the external access point, and use different network wireless names. In fact, given the right modem / router you could rig the external access point on the DMZ side of the modem router, making your own service secure,but giving open access to others. Something to think about